1. Technical Field
The invention relates, in general, to a closed fuel tank system that tightly closes a fuel tank while an engine is being stopped and prevents vaporized fuel from being discharged into the atmosphere.
2. Background Art
Fuel vapor into which automotive fuel is vaporized contains a large quantity of hydrocarbon (HC). Since such hydrocarbon becomes a substance responsible for air pollution, the discharge of the hydrocarbon into the atmosphere has been regulated in recent years. When the fuel is injected into a fuel tank, the fuel vapor corresponding to a volume of the supplied fuel is discharged from the fuel tank. Further, when the fuel is injected through a fuel filler opening by a fuel filler nozzle, air is drawn into the fuel tank by a force with which the fuel enters, and then the fuel vapor of a volume corresponding to the air is further discharged.
An evaporated fuel discharge restraining device disclosed in Japanese Patent No. 4638319 is equipped with a first evaporated fuel passage connecting a fuel tank to a canister and a second evaporated fuel passage (recirculation pipe) connecting the fuel tank to a filler tube located adjacent to a fuel filler opening. The evaporated fuel discharge restraining device adsorbs evaporated fuel (fuel vapor) corresponding to a volume of supplied fuel to the canister. Further, since the evaporated fuel equal to or more than the volume of the supplied fuel is not generated, the evaporated fuel discharge restraining device disclosed in Japanese Patent No. 4638319 discharges the evaporated fuel to the filler tube adjacent to the fuel filler opening via the second evaporated fuel passage, and suctions the evaporated fuel into the fuel tank, and thereby restraining air from going from the fuel filler opening into the fuel tank.
Incidentally, the fuel vapor is generated in the fuel tank even when no fuel is supplied. When an engine is in operation, the fuel vapor is injected into an intake passage, and is burnt and consumed in the engine. Further, when the engine is not operated, the fuel vapor is adsorbed by the canister. The engine is operated, and thereby the fuel vapor adsorbed to the canister is extracted to the intake passage, and is burnt and consumed.
Accordingly, when the engine is operated for traveling, the fuel vapor is consumed at each time. In other words, when the engine is not in operation, the fuel vapor is not consumed. Especially, in the case of a plug-in hybrid electric vehicle (PHEV), an operating rate of the engine is extremely low. For this reason, simply adsorbing the fuel vapor to the canister cannot sufficiently process the fuel vapor. Further, in countries that severely control emission of harmful substances, a mechanism that does not discharge the fuel vapor is required. Taking these into consideration, in the case of the PHEV, it is considered to employ a closed fuel tank system in which a seal valve is installed on a path leading to the canister and the intake passage so as to prevent the fuel vapor from being discharged from the fuel tank.
When the fuel is supplied for the closed fuel tank system, the seal valve is opened, and the fuel vapor pushed out of the fuel tank is adsorbed by the canister. Further, in the closed fuel tank system, when the fuel tank is filled with the fuel to the maximum volume or is so-called “filled up,” the fuel vapor should be prevented from being discharged from a filler pipe and a recirculation pipe. For this reason, when the fuel tank is filled up, ends of these pipes are provided to be kept immersed below a liquid surface of the fuel, i.e. to be submerged.
The seal valve employed in the closed fuel tank system is in a normally closed state, and is opened when the fuel is supplied. To determine that the fuel supply is performed, a lid covering a portion on which a fuel filler opening is installed is provided with a sensor cooperating with the lid. When an electronic control unit (ECU) detects that the lid is opened on the basis of a signal of the sensor, the ECU determines that the fuel supply is performed and opens the seal valve. When it is determined that the lid is closed, the ECU determines that the fuel supply is terminated and closes the seal valve.
Further, the fuel filler opening is mounted with a cap. When the cap is separated to supply the fuel, the lid is opened before that. That is, the seal valve is opened before the cap is separated. Even when a pressure in the fuel tank is higher than an atmospheric pressure by the fuel vapor, the seal valve is opened, and the fuel vapor is discharged to the canister. Thus, since the pressure in the fuel tank becomes the atmospheric pressure before the cap is separated, the fuel vapor is not discharged from the fuel filler opening. When the fuel supply is completed, the cap is attached to the fuel filler opening, and then the lid is closed. That is, the seal valve is closed after the cap is attached. Accordingly, the fuel vapor vaporized in the fuel tank is discharged to the canister through the seal valve until the cap is attached to the fuel filler opening.
However, due to a cause such as a failure, when the seal valve is closed before the cap is attached to the fuel filler opening, the fuel vapor is discharged from the fuel filler opening through the filler pipe and the recirculation pipe. Especially, in the fuel tank that has been filled up, since the filler pipe and the recirculation pipe are submerged in the fuel tank, when the seal valve is closed, the fuel vapor is kept sealed in the fuel tank.
Therefore, when the pressure in the fuel tank is raised due to the vaporization of the fuel, the fuel is pushed up to the fuel filler opening. The fuel has a smaller specific gravity than water, a head from the fuel tank to the fuel filler opening accounts for less than 1 meter. Hence, when the seal valve is left closed without the cap being mounted in the state in which the fuel tank is filled up, the fuel overflows from the fuel filler opening.
Accordingly, the present invention is intended to provide a closed fuel tank system in which, when the seal valve is left closed without the cap being mounted in the state in which the fuel tank is filled up, the fuel does not overflow from the fuel filler opening.